As part of the fabrication process for semiconductor devices such as integrated circuits (ICs), devices residing on a wafer typically undergo a heat treating or thermal annealing process following implantation or doping of the wafer. Annealing may serve several purposes, including physical repair of the silicon lattice structure following doping, and activation of the dopant. Several different annealing processes have been developed and implemented, but each technique carries with it certain disadvantages.
Rapid thermal annealing (RTA) is an annealing process that raises the temperature of the entire silicon wafer for particular period of time using, for example, heat lamps, which radiate the doped wafer surface. However, the RTA process may be time consuming as well as difficult to control, because the lamp turn-on times are variable, and radiative heating may introduce certain thermal control limitations.
Laser annealing is a more recent annealing process, which was developed to provide rapid annealing of one or more of the devices residing on a wafer, as well as greater thermal control. However, laser annealing may also create significant problems, due at least in part to the thermal properties of the laser, the rate of thermal diffusion in the device, and the temperatures generated at the surface of the device. Problems may include, for example, melting of the polysilicon traces, or degeneration of the lattice structure of the device. A need exists, therefore, for a method of laser annealing that addresses at least some of these limitations.